In the jargon of the specific field, under bicycle derailleur gear a front bicycle gearshift is meant. Therefore, in the context of this description, under the term bicycle derailleur gear a front bicycle gearshift will be meant.
Under bicycle derailleur gear a mechanical device is meant that causes the displacement of the transmission chain between different toothed wheels or crowns, for this purpose moving a chain guide in which the chain is engaged. Specifically, the derailleur gear moves the transmission chain between the different crowns associated with the pedal cranks.
Normally, the bicycle derailleur gear comprises a kinematic mechanism in the form of a four-bar linkage with a base body and a mobile body opposite the base body in the four-bar linkage, connected together through a pair of connecting rods hinged to such bodies according to four hinging axes through four pin elements, in which the base body is fixed to the bicycle frame and the mobile body is fixed to a chain guide. The deformation of the four-bar linkage therefore determines a displacement of the chain guide with respect to the frame in the axial direction with respect to the crowns and, in this way, gearshifting.
Relatively recently there has been increasingly common use of bicycle derailleur gears with motorized actuation, i.e. derailleur gears in which, as an alternative to conventional manual actuation, the deformation of the four-bar linkage is obtained through a motor member that is suitably controlled, typically electrically, which moves different parts of the four-bar linkage with respect to one another, deforming it and thus moving the chain guide.
In the development of these derailleur gears, a great detail of attention has been given to the quality of actuation, meaning the ability of the derailleur gear to carry out gearshifting quickly, precisely and reliably over time, at least as well as a conventional derailleur gear with manual actuation.
This requirement is obviously more important the more the derailleur gear is intended to be used in high-level cycling competitions.
In known bicycle front derailleur gears there is generally a toothed sector meshed together with the shaft of the motor member. The toothed sector is made on a lever constrained to the pin element shared by the base body and the first connecting rod in order to transfer to the first connecting rod a rotation about such a pin element controlled by a rotation of the threaded motor shaft.
The Applicant has realised that such a meshed coupling can be subject to malfunctions or create control imprecisions, since it is inevitably exposed to accumulation of residues or dirt during the normal use of the bicycle on the road or, even more so, off-road.
In extreme cases, the meshed coupling is subject to locking or in any case the dirt accumulated in the meshing exerts a contrast action with respect to the action applied by the motor member, introducing delays or imprecisions in the response to the command imparted by the cyclist, a circumstance that can lead to tarnishing the perception of performance that the cyclist has of derailleur gears with motorized actuation with respect to those with manual actuation.
The problem forming the basis of the invention is therefore to avoid the aforementioned drawbacks, in particular by providing a bicycle derailleur gear, particularly a front derailleur gear, which is able to offer and maintain over time excellent performance of control in terms of both precision and response times.
More specifically, the problem forming the basis of the present invention is that of making a bicycle derailleur gear that ensures that the performance of actuation control of the derailleur gear do not deteriorate over time due to dirt or possible residues that accumulate in the motion transfer interfaces between the motor member and the four-bar linkage-kinematic mechanism.